Scanning electron microscopy and Energy dispersive X-ray analysis (SEM/EDX)
quantitative, imaging, small sample areas, vacuum compatible
In scanning electron microscopy (SEM), the sample surface is scanned by a finely-focused electron beam. This is used to generate well focused images. Subsequent X-ray analysis (EDX) makes it possible to determine the elementary composition of very small areas.
Details on SEM/EDX
Element composition, topography, morphology
In Scanning Electron Microscopy (SEM), a sample surface is scanned with a finely focused electron beam. The electron bombardment leads to the emission of low-energy secondary electrons, to the backscattering of high-energy primary electrons and the emission of element-specific X-radiation.
Low-energy secondary electrons come from the uppermost nanometers of a sample. The associated images represent the sample topography with resolution limits in the nm range. The intensity of scattered primary electrons, however, is determined by the mean atomic number of the sample material. Corresponding pictures illustrate the distribution of different materials (material contrast images). The information depth in this mode is on the order of 1 μm. The X-ray radiation - specific for the elemental composition of the sample - is used for chemical characterization. Suitable detectors, determine either the energy or the wavelength of the X-radiation. The measured intensities allow quantitative statements about the elemental composition and distribution. The depth from which the X-rays originate depends on the material and the selected excitation energy. For typical energies of 10 to 20 keV it lies in the µm range.
Samples for SEM / EDX must be vacuum-compatible, whereby modern devices can be used at pressures of approx. 1 mbar (environmental scanning electron microscopy, E-SEM).